Rechargeable batteries, such as those commonly found in vehicles, occasionally require recharging from a source external to the vehicle. Battery jumper cables are usually connected from an external power source, a charged battery or a D.C. power supply, to the discharged battery.
It is imperative that the polarities of the external power source and the discharged battery be properly matched. If the polarities are reversed, the discharged battery will be discharged further, rather than being charged. In this state of rapid discharge, current flows in the cables to such an extent that the insulation or conductor may melt. The discharged battery is subject to internal shorting or even explosion, presenting a great hazard to both operating personnel and equipment.
Thus the need exists for a simple and economical means to prevent improper battery connection in the aforementioned situation. The present invention fulfills that need by providing a visual or aural signal to the operator of the polarity condition prior to power transfer, and a safety circuit which prevents inadvertent application of power should the operator fail to heed the signal.
The prior art is not without examples of the genre, including such patents as Godshalk U.S. Pat. No. 3,387,200, Bach et al. U.S. Pat. No. 3,313,995, St. John U.S. Pat. No. 3,308,365, Rockoff U.S. Pat. No. 3,341,762 and Smith U.S. Pat. No. 3,343,057. There still remains, however, considerable room for improvement.